This invention relates to durability of engine gaskets as utilized in cylinder head applications. More particularly, the invention relates to enhancement of thermal conductivity in gasket materials, with particular emphasis on conveyance of heat from hot spots for improvements in gasket longevity.
The demand for non-asbestos engine gaskets has created a major effort to develop facing materials which are both temperature durable, and cost effective to manufacture. Typically, non-asbestos composites include various bonding agents and filler constituents in order to enhance the physical strength properties of the facing material. Various impregnating agents have been employed in some of the composites for reducing permeability of the composite material and for enhancement of sealing characteristics under high temperature conditions. Such agents tend to be volatilized over a period of time, however, causing a breakdown in the composition integrity. Moreover, to the extent that the gasket may undergo a substantial density reduction due to loss of binder, filler, and other bonding agents, the sealing effectiveness begins to deteriorate almost immediately upon use of the gasket material.
Several efforts have thus been made to aid in the transmission of heat away from combustion opening areas and toward areas adjacent water coolant passages. One such attempt to increase lateral thermal conductivity has involved applying a plurality of heat-conductive foil strips to exterior surfaces of the composite facing material. This has been found effective in the prevention of localized hot-spots. However, some foil materials applied to the exterior surfaces of the facings may be incompatible with certain coating materials which are used as anit-stick and/or anti-fretting agents. In addition, utilization of such overlying thermally conductive materials has created problems with respect to surface damage during installation, particularly where graphite foil is used.